[AIRFLOW-XXXX] Decrease frequency of PR labelling Github Action (#7048)

With the current frequency we are going to exhaust our 2000 free
minutes in about 10 days. We should decrease the frequency quickly.

.github/workflows/label.yml

@@ -25,7 +25,7 @@
 name: Pull Request labeler
 on:
   schedule:
-    - cron: '*/5 * * * *'
+    - cron: '5 0 * * *'
 
 jobs:
   labeler: